What is the Difference Between Serum Iron and Ferritin

The key difference between serum iron and ferritin is that serum iron is the amount of circulating iron bound to transferrin and serum ferritin, while ferritin is an intracellular protein that stores iron in the cell and releases it in a controlled manner.

Iron is an essential nutrient. It has many functions, such as the production of healthy red blood cells. It is a very important part of haemoglobin. The body cannot produce iron on its own, so it has to absorb iron from food and supplements. Normally, iron is transported in the body through a protein known as transferrin. In healthy people, most of the iron in the body is incorporated into haemoglobin in red blood cells. The remaining iron is stored in ferritin. Therefore, serum iron and ferritin help to evaluate iron in the body.

CONTENTS

1. Overview and Key Difference
2. What is Serum Iron 
3. What is Ferritin
4. Similarities – Serum Iron and Ferritin
5. Serum Iron vs Ferritin in Tabular Form
6. Summary

What is Serum Iron?

Serum iron is the amount of circulating iron bound to transferrin and serum ferritin. Serum iron test measures this amount of circulating iron. Normally, 90 % of serum iron is bound to transferrin transport protein. The rest of the 10 % of serum iron is stored in ferritin. Doctors order this test when they suspect an iron deficiency. Iron deficiencies can cause anaemia and other health problems. Usually, 65 % of the iron in the body is in the haemoglobin in red blood cells. Approximately 4 % is in myoglobin molecules. Around 30 % of iron is stored in ferritin or hemosiderin in the spleen, bone marrow and liver. A small amount of iron can be found in other molecules in the cells. None of this iron is directly accessible through testing the serum. Anyhow, some iron is circulating in the serum. Transferrin is a molecule produced by the liver that binds to one or two irons. Circulating iron is mainly bound to transferrin protein. The test for serum iron measures the iron ions that are bound to transferrin and stored in serum ferritin. Moreover, the normal serum iron reference ranges for men are 65 to 176 μg/dL and for women are 50 to 170 μg/dL.

Serum iron test is an important tool for the diagnosis process of conditions such as anaemia, iron deficiency anaemia, anaemia of chronic disease and haemochromatosis.

What is Ferritin?

Ferritin is an intracellular protein that stores iron in the cell and releases it in a controlled manner. It is a globular protein complex. The ferritin test measures the amount of ferritin in the blood. This is an indirect measurement of circulating iron that is bound to or stored in serum ferritin. This protein is produced by almost all living organisms. It keeps iron in soluble and non-toxic form.

Ferritin is produced in most tissues as a cytosolic protein. A small amount secretes into the serum where it functions as an iron carrier. Furthermore, serum ferritin is a diagnostic test for iron deficiency anaemia. The normal ferritin reference ranges in blood for men are 18-270 ng/mL, and for women are 30-160 ng/mL.

What are the Similarities Between Serum Iron and Ferritin?

• Both terms are related to iron.
• They are very important in measuring the total amount of circulating iron.
• Both can be measured by using blood through specific laboratory tests.
• These are diagnostic markers for iron deficiency anaemia.

What is the Difference Between Serum Iron and Ferritin?

Serum iron is the amount of circulating iron bound to transferrin and serum ferritin, while ferritin is an intracellular protein that stores iron in the cell and releases it in a controlled manner. So, this is the key difference between serum iron and ferritin. Furthermore, serum iron is measured through serum iron test, while ferritin is measured through serum ferritin or ferritin test.

The following infographic tabulates the difference between serum iron and ferritin for side by side comparison.

Summary – Serum Iron vs Ferritin

Iron is an important mineral the body uses for growth and development. Serum iron and ferritin help to evaluate iron in the body. Serum iron is the amount of circulating iron that is bound to transferrin and serum ferritin, while ferritin is an intracellular protein that stores iron in the cell and releases it in a controlled manner. Thus, this is the summary of the difference between serum iron and ferritin.

Reference:

1. Soldin, Offie P, et al. “Serum Iron, Ferritin, Transferrin, Total Iron Binding Capacity, Hs-CRP, LDL Cholesterol and Magnesium in Children; New Reference Intervals Using the Dade Dimension Clinical Chemistry System.” Clinica Chimica Acta; International Journal of Clinical Chemistry, U.S. National Library of Medicine.
2.“Ferritin Blood Test: MedlinePlus Medical Test.” MedlinePlus, U.S. National Library of Medicine.

Image Courtesy:

1. “Iron-deficiency Anemia, Peripheral Blood Smear” By Ed Uthman (CC BY 2.0) via Flickr
2. “Ferritin” (GPL) via Commons Wikimedia